OSC 8 hyperlinks landed in #3248, but detectCapabilities() returned
hyperlinks: true in the unknown-terminal fallback. Terminals that
silently swallow OSC 8 (most xterm-compatible hosts, tmux/screen
without passthrough) end up dropping the URL from rendered markdown
links entirely, since the fallback 'text (url)' rendering is skipped
whenever hyperlinks is true.
- Unknown terminals now default to hyperlinks: false.
- tmux and screen (TMUX env, TERM starting with tmux/screen) force
hyperlinks: false even when the outer terminal would otherwise
advertise OSC 8 support. Image protocols also left disabled.
- Added detectCapabilities tests covering the known-capable set and
the tmux/screen/unknown cases.